In applied electrical chemistry, use is made of electrolyzers of various design, which ensure water treatment.
Known in the art is an electrolyzer for water treatment, which comprises a case divided by a diaphragm into an anode chamber and a cathode chamber with perforated electrodes accommodated within them and pressed against the diaphragm, the electrode surface facing the diaphragm is covered with an electrical insulation material, and the perforations are coaxial (USSR Inventor's Certificate No. 882944, CO2F1/46, 1979).
The working surface of this electrolyzer diaphragm is restricted by the area of the perforations in the electrodes, which brings about an increase in weight and size, makes the apparatus more complex in design and requires considerable labour consumption in assembly, disassembly, sealing of the flat pack of electrodes and the diaphragm pressed between them with simultaneous matching of the multiple openings in the electrodes. Because of the non-uniform current distribution, chemical ageing of the diaphragm material and worsening of the electrolyzer characteristics take place.
An apparatus is also known for separate production of water treated in anode and cathode compartments, i.e. catholyte and anolyte, from salted water, used, respectively, as detergent and disinfection solutions in medicine ("Medical electrochemactivator", informational paper 03049 of 27/02/87). The apparatus includes a diaphragm flowtype electrolyzer with plane electrodes and a supply assembly combined with a control unit. The conventional solution is disadvantageous in that it features inadequate hydrodynamics, mixing of the products of the electrochemical reactions when using diaphragms of considerable flow, and also considerable manual labour requirements in the assembly and repair of the electrolyzer with plane electrodes.
The apparatus for water electrolysis (Japanese Patent Application No. 1-104387, CO2F1/46, 1989), most close to the apparatus according to the present invention as to the engineering solution and the result achieved, comprises a cylindrical electrolyzer with coaxial electrodes and a diaphragm therebetween arranged in dielectric sleeves, said diaphragm dividing the internal space into a cathode chamber and an anode chamber. Each chamber is provided with a separate inlet in the lower sleeve and a separate outlet in the upper sleeve of the electrolyzer, said inlet and outlet being in communication with intake and exhaust hydraulic lines for water flow under pressure. The apparatus also includes a d.c. current source connected to the electrolyzer electrode through a switching unit ensuring polarity alteration of the electrodes to eliminate cathode deposit with simultaneous switching of the hydraulic lines, providing for continuous feeding of the solutions from the anode and cathode chambers without mixing thereof. It is noted that the apparatus makes it possible to obtain the electrochemically treated water with bactericide properties.
The disadvantages of the known solution to the problem are large energy losses in water treatment, particularly of water time variable mineralization. The wider the range of possible water mineralization variations, the higher must be the electric power of the used d.c. current source. There are practically no cases when the power of the current source is used effectively to a full extent.
Moreover, the apparatus fails to ensure the stable characteristics of the solutions obtained with little mineralization of the source water.
When a considerable increase or decrease of the apparatus capacity is required, electrolyzers of the corresponding size and, hence, various design must be used. Each particular design implementation features the most effectiveness for the pre-determined operating conditions and cannot be used to advantage in the wide range of mineralization, volumetric flow, specific expenditures of electric energy and other parameters, and also requires individual sets of the basic and spare parts and units, appliances for assembly, adjustment, repair and maintenance. Electrolyzers employing one and the same design circuit but having different geometrical dimensions have different electrochemical characteristics. This requires development of various maintenance rules for each type of a kind of the electrolyzer.
Assembly and disassembly of high-capacity electrolyzers require considerable expenditures of labour and materials.
In high-capacity electrolyzers, the diaphragm and electrodes having a developed surface are subjected to deforming forces with variations of pressure and flow rate of water. This reduces the reliability and service life of the apparatus, causes worsening of the technical characteristics because of distortions of the electrode compartment geometry. Particularly drastic worsening manifests itself when treating water with a low salt concentration, since selfdeveloping processes of local concentrations of the electrolysis products arise which bring about the formation of stagnation zones, local heat build-up and appearance of "spotty" conductivity.